1. Field of the Invention
Embodiments of the present invention relate to a test circuit for testing a signal receiving unit, an image pickup apparatus, a test system for testing a signal receiving unit, a method of testing a signal receiving unit, and a method of testing an image pickup apparatus.
2. Description of the Related Art
An apparatus is known in which signal lines are provided in a plurality of columns and a signal receiving unit (hereinafter, referred to as an SRU) is connected to each signal line. Examples of such apparatuses include a storage device such as a memory, a display such as a liquid crystal panel, a Complementary Metal Oxide Semiconductor (CMOS)-type image pickup apparatus having SRUs for reading signals from pixels, an image pickup apparatus using bipolar transistors, etc. Japanese Patent Laid-Open No. 2000-324404 discloses an image pickup apparatus having a function of testing characteristics of a circuit provided in each column for processing a signal.
In the image pickup apparatus disclosed in Japanese Patent Laid-Open No. 2000-324404, to make it possible to measure the characteristic of an analog-to-digital converter that converts an analog signal output from a pixel into a digital signal, a test signal generator is connected to a vertical signal line. In this configuration, a current is supplied from the test signal generator to the vertical signal line, and the characteristic of the analog-to-digital converter connected to the vertical signal line is measured.
In the configuration disclosed in Japanese Patent Laid-Open No. 2000-324404, the test signal is supplied to pixels in all columns from the single test signal generator, and thus the impedance of an electrical path from the test signal generator to the respective vertical signal lines increases with the distance from the test signal generator. As a result, a great difference occurs in test signal supplied to the respective SRUs as of when the supplying of the test signal to the SRUs is started. Therefore, if the test is performed without waiting for the difference in test signal supplied to the SRUs to become small, an increase occurs in accuracy of the measurement. The test accuracy may be increased if the test is performed after the difference in test signal supplied to the SRUs has become small enough. However, waiting for the difference to become small causes an increase in test time.